Starting a car to find that the engine purrs like a well-fed cat draws a smile from the most hardened of drivers. One way of reducing the engine noise to an environmentally-acceptable standard, consists in layering or stacking heavy materials, such as asphalt, on the floor of the car to absorb the sound. But it is a weighty process, adding kilos onto the overall weight of the car, increases the power and fuel consumption needed to make it go. Making cars lighter is one of the most straightforward ways of cutting their CO2 emissions.
Cars account for around 20% of carbon dioxide emissions in Europe. With increased concerns over climate change, global warming and air pollution over the last decade, car manufacturers have begun to question how they can produce lighter cars to cut emissions, without reducing the overall safety, performance or comfort of the vehicle. In February 2007, the European Commission proposed introducing new legislation that would compel vehicle manufacturers to cut average emissions from new cars by 2012, by improving vehicle technology. Further proposals detailing specific amounts and strategies to achieve them, are expected at the end of this year.
With these factors in mind, sound insulation components have been among the first to be considered for weight loss. These low mass materials are readily available and relatively flexible compared to other car components which they are moulded or formed around. At the behest of French car manufacturers, E!2411 ERTAC set out to reduce the weight of car sound insulation by 30 to 50% while maintaining the same level of acoustic comfort inside the car.
"Instead of using a slow, time-consuming experimental approach to car acoustics, we switched to developing simulation techniques using proven models to predict the behaviour of materials for sound insulation."
Maurice Fortez, Treves, France
To start, preliminary experimental measurements were made on existing vehicles. The project partners then chose to develop new computer techniques to predict the behaviour of insulation parts made from different low mass materials. "The manufacturers drastically reduced the time schedules for new car models, so instead of using a slow, time-consuming experimental approach to car acoustics, we switched to developing simulation techniques using proven models to predict the behaviour of materials for sound insulation" explains Maurice Fortez, director of the main project partner, Treves.
Project partners, Esi, Microdb and Inter AC in France, San Valeriano in Italy and Huntsman Performance Products in Belgium developed techniques to characterise sound at low, medium and high frequencies.
Raw materials were tested for sound insulation, absorption and damping. Sound insulation parts for the car chassis sub-components such as the floor panels and dashboard were also analysed.
The project found that layering compressed felt with a low density kind, reduced the weight of sound insulation by 50%. Using foam textile waste to manufacture parts requiring a certain amount of elasticity, further diminished weight by 25% and cut insulation cost. "Through this approach, we even managed to design thinner treatments for sound insulation in the early stages of the process, with the expected mass reduction," noted Mr Fortez.
According to Mr Fortez, the computer simulation techniques developed through this project provide a faster way to define and quantify acoustic noise behaviour than physical methods, and this will considerably benefit manufacturers. "The simulation of the acoustic performances of car components in the early stages is critical for reducing prototyping costs and improving noise levels inside and outside the car," he says.
Converting the results to a prototype for a real car - a Renault, gave a hefty overall car weight reduction of 6.7%.
"EUREKA really facilitated the partnership that we needed. It helped to bring in and find funding for the acoustic simulation specialists and acoustic experts that we needed"
Maurice Fortez, Treves, France
The virtual results have gone on to be validated on another real car - the Citroen C4. "There is a saving of about 8kg on the weight of the complete car" says Mr Fortez. "The original weight of the insulation was 11.3 kg, but the new technology weighs only 3.4kg", he adds.
A prototype is now being manufactured at Peugeot. Mr Fortez says "Peugeot wants to use this technology for its new 207 model. The company is very interested in significantly reducing car weight and wants to verify the results".
Without EUREKA, Treves would not have been able to launch the project says Mr Fortez. "EUREKA really facilitated the partnership that we needed. It helped to bring in and find funding for the acoustic simulation specialists and acoustic experts that we needed".